The narrative strokes are broad in Cheryl L. West’s Pullman Porter Blues, an intergenerational tale of identity aboard a first-class passenger train, but the show’s impact is hardly blunted by its various melodramatic flourishes. Around the periphery of local playwright West’s musical play about three generations of black men working as train porters are characterizations that aren’t so nuanced — a viciously racist conductor, a redneck stowaway with big dreams, a brassy blues singer with a deeply painful past.

At various moments, each of these characters threatens to transform the show into something fundamentally different — an all-in, unrestrained, near-hysterical drama, writ large across the stage — than it actually is. Instead, it’s the core familial relationship of three men, suffused with unspoken disappointment, love that maybe doesn’t measure up and a firm resolve toward hope that defines the play. Seattle Repertory Theatre opens its 50th Anniversary season with the world premiere of Pullman Porter Blues, and both the tremendous core performances and the musical interludes make for a supremely engaging production.

Punctuated by stirring, bluesy renditions of standards like “This Train,” “Wild Women Don’t Have the Blues,” and “Trouble in Mind,” Pullman Porter Blues finds wide-eyed, eager Cephas (Warner Miller) working his first porter shift in the late 1930s, guided by his simultaneously exasperated and bemused grandfather Monroe (Larry Marshall).

Cephas is a college student with aspirations of becoming a doctor, but he has an unshakeable interest in being a porter as well, polishing glasses and counting napkins with irrepressible enthusiasm. There’s a generational pride in Cephas’ decision to take the summer job, doing the same thing his grandfather has done for the last 50 years, but when his porter father, Sylvester (Cleavant Derricks), discovers his son doing the very work he feels like he’s worked so hard to prevent him from having to do, he’s livid.

West creates some incredibly moving and incisive moments out of the familial conflicts that follow, examining identity and purpose in a massively racially divided world, and allowing her three main characters to breathe as humans, not types. The actors are up to the task too, especially Broadway stars Derricks and Marshall, who both embody deeply conflicted men with unique defense mechanisms.

Even if the rest of the characters aren’t quite so deftly drawn, it doesn’t make them simple deadweight — much of which is due to the actors. E. Faye Butler’s Sister Juba is a showstopper — and not always in the best way — but Butler’s commanding charisma and confident physicality make her a consistent source of delight. Richard Ziman’s conductor Tex is a typical racist scumbag, but Ziman gives the character a cruel sense of humor that adds some dimension. Emily Chisholm is saddled with the most thankless role as hick orphan Lutie, a seeming castoff from Annie Get Your Gun or something, but her pluck and wit help us accept the character as part of this world better than we ought to.

With versatile, immersive scenic design by Riccardo Hernandez and fantastic blues arrangements by onstage conductor and pianist Jmichael, Pullman Porter Blues is very fine season opener for Seattle Rep. The show runs through Oct. 28. Tickets are available for purchase online.